1. Field of the Invention
This invention relates to a slurry for CMP (Chemical Mechanical Polishing), in particular to a slurry for CMP, which is adapted to be employed for forming a damascene wiring consisting mainly of metal such as Al, Cu or W, which is designed to be mounted on a DRAM or a high-speed logic LSI. This invention also relates to method of manufacturing a semiconductor device where such a slurry is employed.
2. Description of the Related Art
In recent years, to meet the trend to further enhance the performance of LSI, the techniques to further refine, densify and multi-laminate the wirings thereof have been rapidly advanced in the manufacture of semiconductor devices. Further, not only the miniaturization of design rule, but also the introduction of novel materials is actively practiced. For example, wiring materials containing Cu as a main component, as well as on interlayer dielectric films (ILD) formed of a low dielectric material such as an organic material or a porous material are being developed now.
In particular, the CMP technique is advantageous in that when it is applied to a dual damascene process where wirings and connecting wirings are designed to be buried in an insulating film, the number of manufacturing steps can be reduced. Further, since it is possible according to the CMP technique to alleviate the magnitude of roughness of the top surface of wafer, the focus margin in a lithography process can be sufficiently secured. Furthermore, it is also possible according to the CMP technique to form a wiring by making use of a material which is difficult to dry-etch such as Cu.
It is demanded at present that the process of forming a metal damascene wiring be enhanced in polishing speed in order to improve the throughput. Further, it is desired, for the purpose of obtaining a high-performance wiring, to develop a CMP treatment wherein the erosion as well as scratching of the metallic portions of wirings and of the interlayer insulating films can be minimized. The term erosion herein means a loss of metal due to the dishing resulting from an over-etching of wirings as well as a loss of metal due to the thinning resulting from an over-etching of insulating films.
The performance of CMP depends largely on a slurry and on a polishing pad to be employed therein. The polishing pad is required to have some degree of hardness for minimizing the erosion. If a polishing pad which is softer than the hard pad which is available from Rodel Co., Ltd. (IC1000-Pad) is employed, it would be difficult to control the erosion even if an ordinary slurry is employed.
Although it is possible to minimize the erosion by making use of the aforementioned hard pad, it may lead to the scratching of wirings and interlayer insulating films or to the peel-off of interlayer insulating films due to the scratching by coarse particles or excessively large aggregates contained in the slurry. Namely, according to the prior art, the minimal erosion and the minimal scratching are related with each other in a state of trade-off. Therefore, it is imperative for the purpose of concurrently minimizing both of the aforementioned erosion and scratching to improve the features of slurry.
A slurry adapted for use in the CMP is formed of a composition wherein polishing particles is dispersed in water. As for the polishing particles made of silica or alumina which are formed by means of fuming method has been conventionally employed. The polishing particles obtained in this manner is featured in that they are low in manufacturing cost and high in purity. Further, the particles produced by means of fuming method is transformed into an aggregate (secondary particles) during the manufacturing steps thereof, and due to the action of the aggregate, the polishing rate is assumed to be enhanced.
However, the particles produced by means of fuming method is very poor in uniformity in diameter of the primary particles so that the secondary particles tends to become too large, thus easily enabling far larger particles to be produced. As a result, it is difficult to strictly control the performance of the CMP.